Marking systems that transport paper or other media are well known in the art. These marking systems include electrostatic marking systems, non-electrostatic marking systems, printers or any other marking system where paper or other flexible media or receiving sheets are transported internally to a an output device such as a finisher and compiler. Many machines are used for collecting or gathering printed sheets so that they may be formed into books, pamphlets, forms, sales literature, instruction books and manuals and the like.
The finisher and compiler are located at a site in these marking systems after the receiving sheets (paper) have been marked. A finisher is generally defined as an output device that has various post printer functions or options such as hole punching, corner stapling, edge stapling, sheet and set stacking, letter or tri-folding, Z-Folding, Bi-folding, signature booklet making, set binding [including thermal, tape and perfect binding], trimming, post process sheet insertion, saddle stitching and others.
The compiler often employs a compiling wall or tray where frictional drive elements hereinafter elastomer paddle wheels or “paddle wheels” (PW) are used to drive sheets (paper) against the compiling wall for registration of the staple or bind edge of a set. If desirable, belts or scuffer wheels may be used, etc. instead of paddle wheels. The force of these frictional drive elements on the sheet is critical and, must be controlled within narrow limits. In the case of Deflection Loaded technologies such as Paddle Wheels, the compiler element drive force has been found to be dependent on the height of the drive element from the sheet In many such finisher compiling systems, the compiler drive element is periodically indexed or raised to attempt to compensate for stack build up. Sheet counting is frequently used as a criteria to index the Compiler Drive element shaft but it does not successfully comprehend curl build up or variations in media weight/thickness. Adding a Stack Height Sensor is also common but expensive.
The compiling capacity and bind edge sheet registration can be compromised with moderate to severe curl on the sheets. The curl can be concave up or concave down and curl build-up generally progressively increases as the paper stack height grows. Excessive curling can cause poor set registration and possibly paper jams or sheet damage.
As discussed above in [003] finisher compiling systems often employ frictional drive elements such as foam scuffer wheels or elastomeric paddle wheels to drive the individual sheets square (deskewed) and against the registration edge. With such compliant drive elements, the normal force on the paper and, thus, the drive force, will increase as the stack height builds up in the compiler tray. As the distance between the shaft and the top of the paper stack decreases, the compression of the foam roll or the deflection of the paddle blades increases and with it the normal and drive forces that are transmitted to the top sheet of the stack.
Over a short distance (change in stack height) this change in force will be minimal. However, with 50 to 100 and 100+ sheet stacks of curled paper of various media weights (gsm), sizes and conditions, the analytical simulation, testing and experience shows that the increase in drive force can become exponential as the stack to drive element shaft gap diminishes. Too little drive force and the sheets will not be properly registered or deskewed. Too much drive force and the top sheets will buckle causing poor set registration and possibly sheet damage or a jam or limiting set size (thickness) compiled.
Differences in media weight and curl will have significant, if not, dramatic effects on the actual stack height build-up, shaft to stack gap and, thus, the drive force. Sheet counting cannot predict or reasonably compensate for the stack height variations across the full range of media weights, sizes and output curl.
A rapid increase in on-demand service to provide large-volume small-scale printing of brochures etc. by use of color/black and white multifunction machines has been exhibited. Even ordinary offices are stepping up their efforts at in-house production of conference paper, simple booklets, manuals and other materials by establishing service departments for intensively processing prints in large quantities. Such customers require post-processing functions such as high-speed/high-precision punching, stapling and paper folding work with simultaneous print output and realization of high-speed/high-quality print output with a high degree of reliability.
“Drive elements or frictional drive elements” as used in this disclosure and claims include any suitable drive element. Also, any number of paddle wheels usually elastomer and any suitable number of paddle wheel blades may be used. The size, type and number of paddle wheels and blades depend upon many variations in the paper used such as size of paper, weight of paper, coated or non-coated paper, paper for color prints, paper for monochrome prints, etc and the specific compiler tray geometry. Also, curl suppressors can be desirably used together with the paddle wheels to improve paper registration. The desired or ideal drive force of the paddle wheels will, of course, vary as the conditions, paper and paper size and other variables change or exist; this ideal drive force can be easily established through simple tests.